1. Field of the Invention
The present invention relates to a push-in type fuse for use in an electric circuit of an automobile or the like. More particularly, the present invention relates to improvements of a push-in type fuse having a fuse body in which a pair of female terminal portions are integrally formed at both ends of a fusible conductor portion having a fusing portion, as well as a housing for accommodating and holding the fuse body.
The present application is based on Japanese Patent Application No. 2000-146693, which is incorporated herein by reference.
2. Description of the Related Art
FIGS. 7 to 9 show related examples of a fuse which is used in an electric circuit of an automobile or the like.
A high rated fuse 1 shown in FIGS. 7 and 8 is comprised of a fuse body 2 formed of a metallic plate, a housing 3 formed of an insulating resin for accommodating and holding the fuse body 2 through an upper opening 3a, and a cover 4 formed of an insulating resin for covering the upper opening 3a of the housing 3.
In the fuse body 2, a substantially strip-shaped fusible conductor portion 2a having a fusing portion C and a pair of terminal portions 2b located at both ends of the fusible conductor portion 2a are integrally formed by a metallic plate.
Each of the terminal portions 2b is a so-called twist-on terminal in which a screwing hole 2c is formed. As shown in FIG. 8, the terminal portion 2b is fastened and fixed by a male screw member (bolt) 10 to a screwing nut 8, which is provided in a fuse fitting portion 7 of a fuse box, together with an LA terminal 9a connected to one end of an electric wire 9 of a circuit on the fuse fitting portion side, thereby allowing the terminal portion 2b to be set in an electrically and mechanically connected state.
FIG. 9 illustrates a fuse body 12 of the so-called push-in type fuse.
In this fuse body 12, a substantially strip-shaped fusible conductor portion 13 having a fusing portion 13a and a pair of female terminal portions 15 provided at both ends of the fusible conductor portion 13 and adapted to be engaged with and connected to a pair of mating tab terminals 14 in a circuit on the fuse fitting portion side are integrally formed by a metallic plate.
Each of the female terminal portions 15 is comprised of a back plate portion 16 formed by extending an end portion of the fusible conductor portion 13, as well as a pair of peripheral wall portions 19a and 19b which respectively extend from both side edges of the back plate 16, are formed by being bent with their tip portions abutting against each other at a position opposing the back plate portion 16, and form together with the back plate portion 16 an engagement space 18 into which the mating tab terminal 14 is fitted.
In the same way as with the fuse body 2 shown in FIG. 7, the fuse body 12 is accommodated and held in an unillustrated housing formed of an insulating resin. A terminal lance 21 which is retained in the housing is formed in the back plate portion 16 by being cut out. A pair of presser springs 23 for pressing and urging the mating tab terminals 14 inserted in the engagement spaces 18 against the respective back plate portions 16 are integrally formed at portions of the pair of peripheral wall portions 19a and 19b opposing the respective back plate portions 16.
In a state in which the fuse body 12 is accommodated and held in the housing formed of an insulating resin, the fuse body 12 is inserted and fitted in the fuse fitting portion where the mating tab terminals 14 are provided uprightly, and as the mating tab terminals 14 are fitted in the engagement spaces 18, the fuse body 12 is set in a state of being electrically and mechanically connected to the mating tab terminals 14.
However, with the high rated fuse shown in FIGS. 7 and 8, the terminal portions 2b are so-called twist-on terminals, and the screwing nuts 8 and the male screw members 10 are required as separate parts.
Accordingly, there have been problems in that the cost becomes high due to an increased number of the parts, and that the operating efficiency of assembly is not good since the operation of tightening the male screw members 10 is required at the time of fitting the fuse.
In addition, with the push-in type fuse shown in FIG. 9, the pair of presser springs 23 for pressing and urging the mating tab terminals 14 inserted in the engagement spaces 18 against the respective back plate portions 16 are formed integrally with the fuse body 12.
Accordingly, in a case where, in order to improve the contact pressure of the mating tab terminal 14 with respect to the back plate portion 16 by strengthening the spring characteristic of the presser spring 23, for example, a material of a high spring characteristic is selected as the metallic plate used, or the thickness of the presser spring 23 is made large, there arise problems in that an increase in the electrical resistance between the pair of female terminal portions 15 can result, and that the formability declines.
Namely, in general, a material having a high spring characteristic has low electrical conductivity, and can therefore cause an increase in the electrical resistance of the fuse body 12. In addition, if the thickness is too large, there is a possibility that a crack may occur in a bent portion at the time of forming the presser spring 23 in the fuse body 12 by bending, so tat the thickness cannot be made extremely large.
Accordingly, the electrical resistance of the push-in type fuse such as the one described above is large, and therefore cannot cope with a high rated fusing characteristic of 100 amperes or higher.
In addition, the electrical path from the back plate portion 16 in contact with the mating tab terminal 14 to the fusible conductor portion 13 assumes a form of detouring the surrounding portions of the terminal lance 21 due to the cutout of the terminal lance 21 which is present midway. Therefore, there has been a problem in that an increase in the current path results, leading to an increase in the circuit resistance between the pair of female terminal portions 15.
Accordingly, it is an object of the present invention to provide a push-in type fuse which makes it possible to improve the spring characteristic of the presser springs at the female terminal portions and make it possible to reduce the circuit resistance between the female terminal portions and to cope with a high rating, thereby overcoming the above-described drawbacks of the related art.
To achieve the above object, according a first aspect of the present invention, there is provided a fuse which comprises:
a fuse body including a fusible conductor portion having a fusing portion, and a pair of female terminal portions integrally formed with end portions of the fusible conductor portion, wherein each of the female terminal portions includes a back plate portion extended from one of the end portions of the fusible conductor portion, and a pair of peripheral wall portions extended respectively from opposite side edges of the back plate portion, the pair of peripheral wall portions being bent so as to oppose tip portions thereof to each other at a position opposing to the back plate portion, so that an engagement space into which a mating tab terminal is insertable is formed between the back plate portion and the pair of peripheral wall portions; and
a presser spring separately formed with the fuse body, the presser spring being attached to a portion of the peripheral wall portions to which the back plate portion is opposed, so that the mating tab terminal inserted in the engagement space is pressed against the back plate portion.
In accordance with the above-described construction according to the first aspect of the present invention, since the presser spring is formed separately from the fuse body, it is possible to select the material and the thickness separately.
Accordingly, as for the fuse body, since a material having high electrical conductivity, though low in the spring characteristic, can be selected, the electrical resistance can be lowered by enlarging the thickness of the fusible conductor portion and the back plate portions.
In addition, as for the presser spring, since a material having a high spring characteristic, though low in electrical conductivity, can be selected, the degree of freedom in the design of the presser spring is enhanced, thereby making it possible to improve the contact pressure of the mating tab terminal with respect to the back plate portion.
Therefore, the fuse body is able to lower the electrical resistance between the pair of female terminal portions and cope with a high rated fusion characteristic even if the fuse is a push-in type fuse.
According to a second aspect of the present invention, it is preferable that the fuse according to the first aspect further comprises a housing in which the fuse body is insertable, and a terminal lance formed on and by partially cutting a portion of the peripheral wall portions which opposes to the back plate portion, wherein the terminal lance of the fuse body is engaged with the housing when the fuse body is inserted in the housing.
In this case, since the cutout of the terminal lance is not present in the current path from the back plate portion in contact with the mating tab terminal to the fusible conductor portion, a linear shortest path is formed, thereby making it possible to further reduce the circuit resistance between the pair of female terminal portions.
The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of the present invention when read in conjunction with the accompanying drawings.